The present invention relates generally to improved methods and apparatus for conducting brain function diagnosis and testing and, more particularly to improved apparatus which can be used for accurately measuring a subject's brain waves during electroencephalography testing.
An electroencephalograph machine, commonly referred to as EEG, is a multi-channel clinical instrument used to detect, measure and display electrical impulses or brain waves of a subject. The brain waves, which are electrical impulses generated by billions of neurons in the brain are detected and monitored during EEG testing by the use plurality of individual electrodes which are adapted to make contact with the subject's scalp in a predetermined pattern or montage, which is well known in the art. Electrical impulses generated by the subject's brain are detected by the electrodes and are transmitted to external monitoring and display devices. The character of the impulses so detected are displayed on a paper stripchart and/or tape and/or displayed on a screen for viewing and diagnostic study and interpretation.
In the prior art, early EEG testing included the display of representations of brain waves or impulses using multi-channel recording devices in which the impulses detected by each electrode were represented as traces scribed on a paper stripchart or tape by a galvanometer type instrument. More updated equipment employs the use of microcomputers into which brain waves detected by the electrodes are applied, and, in accordance with a prerecorded program, are analyzed and displayed for instant visual observation on a CRT and preserved on tape or other magnetic or optical means for more intense observation and study.
Computers used in conjunction with EEG testing, in some cases automatically record and analyze brain waves detected by the electrodes of the EEG and, in more advanced computer systems, prepare detailed reports on the brain waves detected by analysis of the converted electric impulses. Through the use of computer of the detected brain waves, it is state of the art to graphically "map" the brain on the computer's cathode ray tube, i.e. CRT, to check for abnormalities relative to an appropriate reference data base.
EEG testing is not limited to detecting abnormalities in brain function. The technology is used in the therapeutic monitoring of the central nervous system (CNS) effective drugs such as, for example anti-epiletics, cerebrovascular compounds, psychotropics i.e. antidepressants, anxiolytics, antipsychotics, antihistamines and analgesics, etc for determining the effect such drugs have on the brain. EEG testing has also been used clinically to determine the CNS toxicity of peripheral drugs such as cardiovascular drugs, to select the proper psychotropic for a particular patient and/or to determine the development of a progressive cerebral illness by repetitive quantitative EEG testing.
As a research tool, EEG testing has been used to establish quantitive CNS effect of drugs after single and/or multiple doses; for classifying psychotopic properties of drugs; for predicting the "therapeutic window" of psychotropics; and for determining the potency of CNS-effective drugs and determining appropriate dose levels.
Prior art EEG systems are described in U.S. Pat. Nos. 3,518,986; 3,859,988; 4,202,352; 4,213,465; 4,214,591; 4,235,511; Re 30,502; 4,409,987; 4,411,273; 4,424,816 and 4,632,122. Despite the advancement and sophistication of the technology used in current EEG testing the area which appears to warrant more advancement is in electric impulse detection. Hardware used for electric impulse or brain wave detection normally includes some nineteen individual electrodes, particularly located about the scalp. The electrodes are specifically designed to make electrical contact with the subject's scalp or skin and the electric constant of the electrodes must be established on a comparatively uniform, consistent basis in order to obtain a true representation of the brain waves monitored. Placement of electrodes for EEG testing has been a function of measurements of the subject's head, taken by the technician conducting the test, in accordance with the International 10-20 system.
Example of prior art electrodes include those described in U.S. Pat. Nos. 2,872,926; 3,151,619; 3,170,459; 3,187,745; 3,295,515; 3,469,577; 3,528,408; 3,580,239; 3,602,216; 3,623,479; 3,669,110; 4,033,334; 4,051,842 and 4,632,122.
As a review of these patents will demonstrate, the state of the art relative to electrode design and placement for EEG systems has not advanced in step with the related hardware and software used in analyzing the EEG test results. For most electrode designs, location and placement of the individual electrodes are on a trial and error basis and consistency in placement of electrodes remains a problem. The securing of the plurality of electrodes to the patient's scalp is a cumbersome, messy and time consuming activity which most often requires a gross inconvenience to the patient and may require substantial training on the part of the technician. The amount of time required to properly locate and connect a set of electrodes at nineteen (19) different location on a patient's scalp, determined in accordance with the International 10-20 system can be substantial, often taking as long as thirty to forty-five minutes.
In most cases, the chances of locating electrodes in exactly the same positions on the scalp of the sam patient during repetitive testing, is difficult, problematic and highly unlikely, thus tending to adversely effect the reliability of the results of repetitive tests on the same patient. Moreover, the chances of obtaining and maintaining good, consistent electrical contact between the electrodes and the scalp at all multiple locations can prove difficult due to differences in skull size, shape and the amount and texture of hair cover of different patients or subjects.
A more recent development in the hardware relating to electrodes used in EEG tests includes the use of a headset, fitted with a plurality of electrodes, suitable for placement on the head of a patient or subject to be tested. The electrodes are mounted in the headset and are biased, by the use of resilient material, against the scalp of the patient. Independent positive orientation of each electrode mounted in a helmet is achieved by the use of a gas pressure system.